CLEANUP: stconn: rename cs_{check,strm,strm_task} to sc_strm_*

These functions return the app-layer associated with an stconn, which
is a check, a stream or a stream's task. They're used a lot to access
channels, flags and for waking up tasks. Let's just name them
appropriately for the stream connector.
diff --git a/src/mux_h1.c b/src/mux_h1.c
index 87a2970..0c107fa 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -1418,11 +1418,11 @@
 	struct proxy *other_end;
 	union error_snapshot_ctx ctx;
 
-	if ((h1c->flags & H1C_F_ST_ATTACHED) && cs_strm(h1s_sc(h1s))) {
+	if ((h1c->flags & H1C_F_ST_ATTACHED) && sc_strm(h1s_sc(h1s))) {
 		if (sess == NULL)
-			sess = __cs_strm(h1s_sc(h1s))->sess;
+			sess = __sc_strm(h1s_sc(h1s))->sess;
 		if (!(h1m->flags & H1_MF_RESP))
-			other_end = __cs_strm(h1s_sc(h1s))->be;
+			other_end = __sc_strm(h1s_sc(h1s))->be;
 		else
 			other_end = sess->fe;
 	} else